Overflow trunking system.



C. C. ABRADBURY. ovERFLw TRUNKlN SYSIEM.

APPLICATION FILED JULY 25.1914. L

c, c. BRADBURY.

OVERFLOW TRUNKING SYSTEM.

APPLICATION min JULY 25.1914.

1,1 61,602., mam Nov. 23, 12H5.

2 SHEETS-SHEET?. Y

Q, i "Q Y UNiTED STATES PATENTQFFICE CLIFFORD C. BRADBURY. OF MOUNTVERNON. NEXV YORK. ASSIGNOR TO XVESTERN ELECTRIC COMPANY. OF NEW YORK.N. Y., A CORPORATION 0E ILLINOIS.

OVERFLOW TRUNKING SYSTEM.

Specification of Letters Patent.

aielited Nov. 23. 1915.

To ./Z lello/li if muy conciliar:

Be it known that l. tLiii-'oiin C. Bimonijiii. a citizen ot' the l'nitedStates. residing at Blount Vernon. in the county of vWestchester andState of- XewfYork. hay i.ii- \ell.ted :l' certain new and usefulimprovenlcn't iii (lyertlow Truiiking Systeiils. of which the followingis a full. clear. concise.

'and exact description.A

This invention relates to overflow tljllilking systems for automatictelephone ex'- chaliges.

llxperience has shown that whereas a `roup ol .suhscrihers wllooriginate on their lilies a certain average llumher ofcalls per hourreiiuire a certain nninher of trunks to accommodate the silliultaneouscalls arising from this group of suhscrihers. a larger grou i otsuhscrihers originating an average s t oi twice as many calls per hourwill require coiisiderahly less than twice as niaily trunks toaccoiilmodate the simultaneous calls from the larger group. Likewise. agroup otsul)- scrihers originating all average of 2%. l. n times asiuany calls per hour a's the small group -will reipiire ill each caseconsiderahly less than 33. i. 3. n imes the numlicr of trunksreoliired'hy' the siliall group to accoiilnlodatc the siillultaneouscalls. 'l`he al'- rangeilieiit ot lines. therefore. which would heideal. would he one in which all of the` 'the cumllel'soiiieness of theapparatus required.

lt is the oliject of the present invention to proyidc a .system of linesand secondary .switches hy means ol' which the allure pointedout idealarl'angcilieut is approached witll apparatusjwliich permits thesnhscrihers` lilies to he arranged in small groups in a manner which hasproven economical in practice.

rThe method of carrying out my invention is illustrated iii thcaccompanying drawings, Figures l and 2. The various circles 0repthe'li'rst idle trunk.

resent suhscrihers` stations or other sources tor originating calls."l`hc arcs oll circles T and lU'with their associated arms, reprcseui'l'espectiycly primary and orcrllow switches for distributing calls toany one ot' the trunk circuits-extending either tothe secondary switchesi! represented iu thc drawing hy siiiall rectangles. or to otherorcrllow switches 1t). The switches T and ll) are ot any well knowntype. hy means of which connection is automatically estalilishcd withillustrations of these are iluillerous in the art of alltolnatictelephony. aild no description of any specilic type ot' switcll isconsidered necessary" t'or the purposes of this spetilication.

The primary switches'. of which tllere is one for each subscriberslille. are arranged iii groups designated as the 1st, 2nd. 33rd, 4th.5th. tih. ith and so oil to the nth groups. each group colllprisiiigapproximately lll() suhscrihers` lilies. There 4may he any desiredlinin'her ot these groups. the 11th grolip hearing the same relation tothe 1st. 2nd.

y ird aild Jith groups as each group hears rto the four groups followingit. so that all groups taken together forni a cycle. `all groups otlwhich hear-similar relation to other succeeding groups ill the cycle.llacll of these groups serves suhscrihers` lines or other sources otoriginating calls sullicient in nunil'ier to originate. 'except underalmoriiial circiuustances. calls requiring a maxiiilllin of telisimultaneous connections. lach primary switch ot each group has multi-Apled to it six trunks extending to Six diil'en eiltI secondary switches5. aild in addition thereto each primary switchot` each group haslluiltipled to it tour trunks extending lto l'our auxiliary or oycrllowswitches 1U. haying access respectively to the trunks of each ot t'oilrsucceeding groups. `il'ith this arrangement cach group ot' originatinglilies has access to six secondary switches ol' its own particulargroup. alld ill addition thereto. through its lour additional trunklines and four orcrtlow switches. has access to all of thc secondaryswitches of the tour succeeding groups and through the last fourtrunkslof cach of these groups to the secoinlary switches ot' othergroups, and so oil through all of the groups. including the nth group.Thus-any line may. under proper conditions. vconnect with any secondaryswitch of the exchange.

i as met i9..

While all of the lines of the exchange have access only (6a) secondaryswitches, itdoes not follow that in order for-.all of these secondaryswitches be used simultaneously the groups must originate six calls to agroup', 'or example, originate ten simultaneous calls which wou use upall 4of its own secon four of the trunks extending overflow i0 switchesof other groups'. Under favorable conditions the second, or any otherone group shown, may` at the' saine time voriginate any number of callsup to nine, and t e 6th group, or any may again originate ten calls. inient permits a large vber of calls originat' This arrange- 4 he numingwithout, at any time, I of the number of accessible secondary switcheswhich exper ience shows are redeprivingl any group quired tosatisfactorily take care of the traffic which is liable to arise in thatgroup. An additional feature of my invention prevents the primaryswitches, of a particular group, from unnecessarily establishing aconnection with an idle overflow switch in another group when all thetrunks serving this overflow switch' are busy. is prevents anunnecessary tying up of inter- 30. switch trunks whenA no connect' oncould be established even- .though an id switch were found. For thisvpurpose eac of the over ow switches is provided with a normal contact 11"and an off-normal con- The secondary switches are each -equippedwithtwo` off and o 4o normal contacts 13 of the same group, an

the four (iE-normal contacts 12 of the rst, second, third and fourthoverow switches respectiyely of the first, second, third and fourth.succeeding groups. The mova e element of the last ofi-normal contact 12is wired to ground or test The off-normal contacts secondary switchesare connected i in a singlecircuit terminating in a grounde a0 battery.The other end of this circuit is connected in parallel through relays15, one for each grou to the ground terminal of armatures o the relays1a ground, or testA b5 potential, and the make contacts are i inparallel to the norma overflow switches 10 of the particular group'associated with each relay. The manner in which these circuits preventthe unnecessary so tying up o interswitch'trunks will now beillustrated. Whenever the number of'simultaneous calls originated in anyequal to the determined maximum number of simultaneous calls allowed pergroup, ten

per group inthe system illustrated, all the other group beyond that,

group the last overflow'trunk available.

' vantage by way trunks to the secondary switches directly available forthis group as well las the trunks leading to the overflow switches whichserve this group directly will be busy. In this case all the trunkoutlets from suc a grou will be busy, and it is therefore imortant thatnone of the hes ofganyfo` the other groups shall select thel trunksy'leading to the overflow switches o the busy group. Such a connectionwoult prevent the call from going to a group in which an idle trunkcould be'found and wouldfalso cause one of the switches of the tocontinue to unnecessarily hunt ls of this group. l of the trunks leadingto theV secondary and overflow switches o any group are usy, bemaintained on the normal contacts o the overflow switches of the vbusygroup. The ,method by which this is accomplished `canv be illustrated tothe best advantage by assuming. a concrete condition. hus, if .all ofthe trunks extend' the first grou are busy, a circuit will beestablished from the ground at the off-normal contact 12 of the lastoverflow switch of the 5th group,

to and through this off-normal contact and the off-normal contacts 12 ofthe third, secgroups, respectively, through-the offnormal contacts 13 ofthe secondary switches" ofthe first group and then to the normalcontacts 11 of 'the over` flow switches of the first group in parallel,establishing the busy condition on all of the trunks leading ,to theseswitches. Thus in the 5th group, the third overflow trunk `in the sixthgroup, the second overflow trunk in the seventh group andthe firstoverflow trunk in the lnth group' will be connected to the busypotential. The switches in these groups wi therefore not select a trunkto the first group the first group is t the moment a trunk of the firstgroup becomesl available, by reasoii'o the return to normal .of one ofthe switches of the first group, the established busy circuit connectedto the overflow switch normal contacts 11 of the I'first group wil beinterrupted at one of the off-normal contact: 13 or 12 of they secondaryor overflov switches 'serving the group. i

An originating call in any group wi never proceed beyond its individualprimar switch unless there is an available secondai switch in its own orone of the other group and in the latter case av circuit through ioverflow switches of the groups leading the idle'secondary switch mustalso be ava able.l This can be described to the best 2 .ofillustration.` hus, suming conditions in which each group w theexception of the ath group has-ori ciatvd with thv calling linv wouldhunt and svlvct thc trunk lvading tothe first orvrflow switch in thvsvt-ond group. which in turn would hunt and svlvct the -first oyvrliowswitch in thv third group and this provvss would continuv to thv nthgroup, 'l`liv oyvrllow switch svlvctvd in the -1th group would thenconnvct thv only'ayailahlv idlv svcondary switch in the systvin to thecalling suliscrilivr in thv tirst group.

it `timing now a' condition in which a call is originated in thv tirstgroup when all thv secondary switch'vs iu thv systvni arv busy. and atwhich tiiiiv vithvr no oyvrtiow switches or only a part ot' thv oyvrtlowswitchvs arv .husy. This condition would arisv vithvr when vacli grouporiginates six calls. thus utilizing v\'vry ayailahlv svcondary switchin thv systvni l'or calls. six in numhvr. originating in cach group. ,orwhvn thv toal'nuinhvr ot' calls vtluals thv nuinlivr otl secondaryswitchvs and arv distriliuti-tl jtrom thv various groups in such amanner that thv oi'vrllow trunlts arv not vxliaustvd. condition of thishind may ovi: casioiiully oi'till :liitl is dcsci'ilivil to show thatwith thv svvvrvst hind otl trallic conditions thvrv will liv nounnvcvssary tying up i' Y v ot truiilts. hut ou thv contrary. thvprimary switch associatvd with thv calling suhscrilafr .q will hv thvonly switch which hvconivs opvratiyv. rl`liis condition will continuvuntil onv ot' thv svcondary switchvs in thv systvin is rvlvased. atwhich tiinv this switch will hc svlvctvd as prvriously vxplainvd.

llaying assuinvd thatall thv secondary switchvs arv husy. it thviifollows that thv svrivs circuit through thv oli-normal contacts il isclosvd. 'thv now closvd ott-nornial contacts 1l couiplvtv a circuitthrough all thv i'vlays l5 in parallvl. 'lhv opvration ol' vach onv ot'thvsv rvlays connvcts thv husy potvntial with thv normal contacts l1 ofthv oyvriiow switchvs ot thv group associatvd with cach rvlay. rl`hisplacvs thv busy test potvntial on the normal contacts l1 ot' all theauxiliary switchvsizi thv system not actually in usv. and as all thesvcondary switches in thv systcni are also husy. every switch contact inthe systvni is connvctvd to the busy pot'vutial. lndvrthese'circun'istances the wipvr ot' any culling suliscrihvfs primaryswitch linds all ot' thv switch contacts lousy and may hv arrangvd tocontinue to hunt or not to start limiting. or to give the subscriber alousy until one of the seconrhirv ,switches is rvleasethltliereliyopening the serivs circuit through its oit-normal contacts ll.whiclrw'ill reinoyv thv husy potential from thv normal contacts ll ofall of the orvrl'low switches 'not actually in use. The call will tlivnproceed through the idle oyertlow switvhvs until the released svcontlaryswitch is svlvctvd.

Uhriously this invention is not limited to thv spvciliv vnihotliinvntherein shown and dvscrihvd. hut, is capable ofI inany variations andapplications without departing from its spirit and scope. i

What claimed is: v

t. In a trunliing system, the combination with incoming and outgoingcircuits` oit' automatic means for establishing connection hvtween anincoming circuitandan idle outgoingcircuit, said outgoing vircuits'hvingot'- two classes and so arrangvtl tllat the circuits of one class willall he selected hvt'orv any of the circuits ot' thv other class are.svlv-'ftvth` a svlvctor switch for vach ot' the outgoing circuits of thvprvfvrrvd class. each of the otlivr outgoing circuits appearing as anincoming' circuit iu aiiotlivr group and at said group haring avcvsstoother outgoingr circuits ot two classvs .similar to thv outgoingcircuits' of thv lirst group.-

2. lu an automatic tvlvphonv system. suhscrihvrs liuvs arraugvd ingroups` lirini-.iry switclivs for said suliscrihvis` lines. trunli linvstvrniinating in said primary switchvs. svvondary switchvs associatvdwith a part ot said ti'unli linvs. orcrllow switchvs assoviatvd with thvivniaindcr ol'v said trunk linvs. said oivrtlow switchvs in vach groupharing accvss vithvr dirvctly oi through othvro\ci'l lo\\' switchvs tothv .svcoiitlary switchvs of any group.

Il. ln an automatic Ivlvphonv systvin. thv coniliination withsuliscrilicrs` linvs arrangvd in groups. a primary lswitch i'orA vachsul|- scrilivr`s line. svcoudary and oyvrllow switchvs asso'ciutcd withvach group. means lor connvcting a calling linv in any group with thvtirst idle secondary switch in that group. or it' thv svcondary switchvsof that group arv husy with the lrst accvssihlv idlv oyvrllow switch olone ot' thv othvr groups. invans to connvct said oyvrllow switch withany svcondary switch ot' thv selected group.y or it' thv secondaryswitches of that group arvy husy witlian idle oyvrllow switch of one ot'the other groups. and means to connect the orertiow switches of eachselected group with the secondary switches of that group? .or if thesecondary switches of vthat group are husy with an idle oyerow switch ofone of the other groups.

l. ln an overflow trunking systm. originating lines, primary. secondaryand overtlow s'witchvs, .all arranged in groups,` trunks niultipled. tothe primary and oyertlow Qwiinhvs of each group and terminating in lOtthe secondary switches of that group, other trunks multipled through theprimary and overflow switches of' each group and terminating in similaroverflow switches of other groups, whereby an originating line may bcconnected through one of the trunks of' its group to a vsecondary switchof its group, if' one is idle, or to a selectable overflow switch ofsome succeeding group, and through the selected overflow switch to asecondary switch of the selected group, if one is idle, or anotherselectable overflow switch of some succeeding group, and through this orsome succeeding overflow switch to the first available idle secondaryswitch.

5. In an overflow trunking system, the

W.combination with subscribers lines arranged in groups, of primaryswitches for said subscribers lines, trunk lines terminating in saidprimary switches, secondary switches associated with a part of saidtrunk `lines and overflow switches associated with the remainder of saidtrunk lines, said primary switches serving to connect a subscriber inany group with the first idle secondary switch of' that group, or withan overflow switch of another' group if the secondary switches are busyand said selected overflow switch serving to connect the subscriber withthe first idle overflow switch of one of the succeeding groups providedthe secondary switches of the selected group are busy and an idle trunkby way of overflow switches to the group containing an'idle secondaryswitch is available, and means to prevent a calling line from beingconnected with an overflow switch when there is no idle secondaryswitch.

In an overflow trunking system, the combination with subscribers linesarranged in groups, of primary .switches for said subscribers lines,overflow switches in each group selectable by the primary and overflowswitches of' other groups, secondary switches accessible to the primaryand. overflow switches of all groups, and means to prevent asubscriber-s line from being connected with an overfiow switch when allthe secondary switches in the system are busy.

'7. In an overflow trunking system, the combination with subscriberslines arranged in groups, of primary switches for said subscriberslines, secondary and overflow switches associated with the primaryswitches and means to cause the overflow switches in all of the groupsto test busy whenever the secondary switches in all of the-groups arebusy.

`8. In an overflow trunking system, the combination with subscriberslines arranged in groups, of primary switches for said sub` scriberslines, secondary and overflow switches'l associated with the primary 9.In an overflow trunking system, the

combination with subscribers lines arranged in groups, of primaryswitches for said subscribers lines, trunk linesterminating in saidprimary switches, secondary switches associated with a part of saidtrunk lines and overflow switches associated with the remair-.derofi-'said trunk lines, said primary switches serving to select the firstidle secondary switch of that group or an overflow switch of anothergroup if the secondarye switches are busy, said selected overflow switchserving to select the first idle over'- flow switch of one of thesucceeding groups provided the secondary switches of the se,- lectedgroup are busy, and means to maintain a busy potential on the trunksterminating in the overflow switches o any group whenever all the trunksextending from said group are busy. A

10. In an overflow trunking system, the' combination with subscriberslines arranged in groups, of-primary switches for said subscriberslines, trunk lines terminating -in said primary switches, secondaryswitches for each group and overflow switches of other groups connectedto the -trunk lines of each group, and means to maintain a busypotential on all of the trunk lines of a group when the secondaryswitches of that group are busy andl there is no available` trunk fromany of the overflow switches in other groups. to which the overflowtrunks if that group extend.

11. In an overflow trunking system, the combination with subscriberslines arranged in groups, ofprimary switches for said subscribers lines,trunk lines terminating inl said primary switches, secondary switchesfor each group and overflow switches of other groups associated with thetrunk lines of each group, and means to delay the progress ofinterswitch trunking at the originating .primary switch unless there isan available trunk to an idle secondary switch in one of the groups ofthe system.

12. In a trunking system, the combination with a group of originatinglines', of a plurality of trunk line groups, automatic means forestablishing connections between an originating line and idle ones ofthe trunk lines of its group, secondary switches con' nected withcertain ones of said trunk lines, the other of said trunk linesextending as originating lines to other groups of trunk lines and thereterminating in automatic meansfor establishing,"connection between saidtrunks of the first group and lidle trunks f with idle trunks:

of the other groups, :i part of thetrnks of the otherv `groups likewiseterminating inI secondary switches.'

13,111 a trunking systemen plurality of originating lines, twin groupsof trunk lines," similar antomatidsecondary switchesfor' a.' part ef thetrunk lines'of eaclfgro'up', onelof; the trunk'lines of one groupterminatir'lg-` as` Y l anbriginating line in .the other group,' andautomaticmeans to connect originatlng lines 14.l In a trunking systen1,the combination with a pluralityof originating lines, of a mov-v ablecontct Wiper` for` each line', a plurality of sttionary trunk contactsfor' engagement by saidfwipers, a pluralityl of overflow trunkcircuits,A a moveble Contact wiper. forl each oyerlow trunk circuit,-'ayplur'zt1ityofstaf' tionary trunk Acontacts for eng'g'agezn'ent' bysaid'fyipers, said stationzily-contactl being multiply .connected 'tothe stationary trunk' ontats-t before mentioned, secondary lSwitchesrcon'nected toeetam of saidrmnltipledztrunk, contacts, othermovable', contacts conneeted 'toi they remainder 'of said Inulti'- 2pled' trunk'contacte,I ndfftller multipled trunk oonta'cts ae'essibleto' sind' latter movable Contacts.

